This is to provide an aqueous metal surface treatment agent for a lithium ion secondary battery which can improve interlaminar adhesiveness between a metal member and a resin coating layer such as a film or a coated film, and solvent resistance without using trivalent chromium.The aqueous metal surface treatment agent for a lithium ion secondary battery comprises a polyvinyl alcohol resin containing 2 to 15 mol % of a 1,2-diol structural unit represented by the formula (1): Having a degree of saponification of 90 to 99.9 mol % and an average degree of polymerization of 250 to 3000; and a metallic crosslinking agent.